1. Field of the Invention
This invention relates to respiratory humidifiers and more particularly but not solely to respiratory humidifier conduits used in the breathing circuits of humidifiers to provide humidified gases to a patient or other person in need of such gases.
2. Description of the Prior Art
In order to supply gases, for example humidified gases, to a patient or other person in need of such gases, flexible conduits have been used both from the gases supply to the patient (inspiratory conduit)and from the patient back to the gases supply (expiratory gases). When the supplied gas is a humidified gas, it is desirable to minimise the amount of condensation occurring on the inner walls of the conduit as this condensation soon accumulates requiring regular draining. Some existing respiratory humidifier conduits incorporate heating wires in an attempt to reduce condensation and also to assist in the control of the temperature of the humidified gases within the conduit being delivered to the patient.
An example of a respiratory humidifier conduit incorporating a heating wire is disclosed in our prior U.S. Pat. No. 4,708,831 to Elsworth et al. The heating wire disclosed is a looped heating element with the two free ends of the loop emerging from the conduit for connection to a source of alternating voltage on the humidifier. Voltage is applied across the ends of the heating wire and, as the heating wire is looped, the voltage at the point closest to the patient has reduced to around half the input voltage. It has been found that, in some medical applications where sensitive monitoring equipment is positioned on the patient, although the voltage at the point closest to the patient is very low (for example 11V.sub.rms), the electric field produced from the heater wire can, in some instances, be registered by the monitoring devices. It has been found that this is usually an intermittent problem and is dependent on many factors, such as the frequency of the heating wire voltage and the sensitivity and quality of the medical monitoring device and connections thereto.